Light emitting diodes (“LEDs”) have many advantages over conventional light sources, such as incandescent, halogen and fluorescent lamps. These advantages include longer operating life, lower power consumption and smaller size. Consequently, conventional light sources are increasingly being replaced with LEDs in traditional lighting applications. As an example, LEDs are currently being used in light bulbs, flashlights, traffic signal lights, automotive exterior and interior lights and display devices.
A typical LED includes an LED die mounted on a substrate, such as a leadframe, and encapsulated in a molded transparent lamp package. Since the light output of an LED is limited, the LED die may be mounted in a reflector cup formed on the substrate to collect the light emitted by the LED die and direct the light upward toward the top of the transparent lamp package. Moreover, the transparent lamp package of the LED may have a domed top, which functions as a lens to focus the light emitted from the LED die.
LED-based illumination devices have been developed that use a number of LEDs to produce sufficient light output comparable to conventional light sources. The LEDs are electrically and structurally attached to a printed circuit board (PCB), which includes circuits to provide driving signals to the LEDs. The light from each LED is emitted in a substantially narrow field of view in a direction perpendicular to the surface of the PCB. Thus, the combined light from all the LEDs has a small angle of illumination. However, there is a need for a light source that provides a wider angle of illumination, and even a spherical illumination. Consequently, some LED-based illumination devices include a spherical cover that scatters the light from the LEDs to produce a wider angle of illumination.
However, these LED-based illumination devices can at best produce a hemispheric illumination. Furthermore, the intensity of light from such an LED-based illumination device tends to be non-uniform. Thus, what is needed is an LED-based illumination device that can provide a wide angle of uniform illumination.